1. Field of the Invention
This invention relates to webbing lock devices each used in a seatbelt system for protecting an occupant in the event of an emergency situation of a vehicle by locking an occupant restraining webbing, and particularly to a webbing lock device for directly clamping the intermediate portion of the webbing to lock the webbing, thereby bringing the occupant into a restrained state.
2. Description of the Prior Art
Heretofore, there has been proposed a webbing lock device for bringing an occupant into a webbing-restrained state by directly clamping the intermediate portion of an occupant restraining webbing of a seatbelt system in the event of an emergency situation of a vehicle. The webbing lock device of the type described is adapted to actuate a pair of clamp members by a tension generated in the webbing in the event of an emergency situation of the vehicle to thereby directly clamp the intermediate portion of the webbing. By this arrangement, the webbing lock device of the type described is advantageous in that no high tension acts on the webbing wound in layers into a takeup shaft, and moreover, the condition of loosely wound-up webbing is prevented from occurring, which would otherwise allow the portion of the webbing wound in layers to be greatly extended out, thereby improving an occupant restraining performance.
However, in the webbing lock device of this type, facing surfaces of the pair of clamp members are formed into corrugated shapes so as to increase frictional forces between the webbing and these facing surfaces. More specifically, in order to lock the webbing from its side of the takeup shaft to its side of the occupant restraining portion under a uniform clamping force between the corrugated shapes complementary to each other which are formed on the facing surfaces of the pair of clamp members, it is essential to provide the corrugated shapes with considerably high accuracy. Additionally, there is a possibility that errors in dimensions during assembling lead to the lack of a uniform clamping force during locking, thus causing a variability in locking performance.